1. Field of the Invention
The present invention relates to an air bag system that protects an occupant of a motor vehicle in the event of a crash. More particularly, it relates to an air bag system that provides a variable-size inflatable volume and a variable-output gas supply to produce optimal protection for the occupant regardless of whether he/she is wearing a seat belt and regardless of whether the crash speed is moderate or high.
2. Background of the Invention
U.S. Federal Government safety regulations (Federal Motor Vehicle Safety Standard (FMVSS) 208) require that motor vehicle air bags protect unbelted front seat occupants in frontal barrier crashes where the vehicle is traveling at 30 mph at impact. In order to do so, air bags must be relatively large, hard, and inflate rapidly. Collectively these characteristics describe an air bag that is referred to herein as an aggressive air bag. Although required by U.S. law, on some occasions, aggressive air bags can cause serious or even fatal injuries.
This is all the more unfortunate because the U.S. government's own National Accident Statistic Study (NASS) shows that 98 percent of accidents causing air bag deployment occur at crash speeds at 30 mph or below. (NASS is an ongoing statistical study of vehicle accidents conducted by the National Highway Traffic Safety Administration (NHTSA) of the U.S. Department of Transportation.) Furthermore, the study shows 80 percent of air bag deployments occur below 20 mph. In addition, it points out that approximately 75 percent of front seat occupants now wear seat belts. Thus, only 0.5%, of the population (assuming that only 25% of the crash victims for accidents occurring at crash speeds of 30 mph are not wearing seat belts) actually need an air bag that complies with the current government standard. Everyone else is being subjected unnecessarily to an aggressive air bag deployment.
The air bag system that is installed in most of the vehicles currently sold in the United States does not distinguish between, or accommodate, the different protection needs of the occupant who is wearing a seat belt and one who is not. Instead, because of government safety standards, it is constructed purposefully to protect the unrestrained occupant in a severe crash from hitting the car interior by aggressively deploying a large air bag at a high inflation rate.
An aggressive air bag can protect the occupant from hitting a structural part of the vehicle's interior. However, to do so he/she will very likely be struck by the air bag, and the potential for abrasions or more serious injuries is high. If restrained with a seat belt, the occupant is less at risk but often is still forcibly struck by the deploying bag. If unrestrained, the occupant travels faster and more forward before being struck by the deploying bag and experiences even greater harmful effects of deployment forces.
Various means have been devised to attempt to overcome the potential hazards associated with the use of large, high aggressivity air bags. Some of these devices are as follows:
U.S. Pat. No. 3,879,056 discloses an air bag with a belt-like restraining member that limits the extent of deployment When the occupant impacts the air bag, the restraining member breaks, which reduces the bag's air pressure and the rebounding force imparted to the occupant.
U.S. Pat. No. 3,990,726 discloses an air bag with a seam that opens when the occupant hits the air bag, thus lowering bag pressure and rebounding force.
U.S. Pat. No. 5,240,283 discloses an air bag with attached auxiliary bags which inflate with gas that is forced into them from the primary bag when the occupant strikes the primary bag.
U.S. Pat. No. 5,282,646 discloses an air bag with a valve that controls inflation of two internal chambers. The chambers communicate via two openings. The first is always open and permits immediate flow of inflation gas from the first chamber, which is coupled to the inflator, to the second chamber, which is nearer the occupant. The other opening has a mesh covering and is normally closed by a flap that is also attached to the occupant-contacting wall. As the second chamber expands via inflation through the first opening, the occupant-contacting wall moves toward the occupant. When this wall reaches a predetermined expansion, the wall pulls the valve flap open and exposes the second opening. The air bag continues to inflate to its final volume; that is, to the extent the occupant-contacting wall can move toward the occupant.
All of the above patents relate to air bags that can significantly change volume upon occupant loading but which have a fixed-volume gas generator supply. Because of their fixed-volume gas supply, these air bags can either adequately inflate the first volume or the bag's largest volume, but not both. If the gas in an air bag of this type of system adequately inflates the first volume and, upon occupant loading, presents a larger volume, the air bag will behave as if the first volume ruptured which would leave the occupant effectively unrestrained. Hence an air bag system constructed in this manner could only open in such a way that the gas would vent into the larger volume upon occupant impact at a rate equivalent to that of typical vented air bag designs in order to be an effective restraint. To be effective, a single gas generator air bag system can have only a single-volume air bag. Of course, if small changes in volume were allowed, a single gas generator could be used, but these small changes could never be used to accommodate differences in the effect of occupant loading that occur in belted versus unbelted occupant or moderate-speed crash versus high-speed crash situations. The above-cited patents pertain to what are hereinafter referred to as variable-volume, fixed-inflation designs.
U.S. Pat. No. 5,074,583 discloses a passenger-side air bag system including a seating condition sensor that detects the temperature of the passenger compartment and seating condition of a passenger with respect to seat position, reclining angle, passenger size, passenger posture, and seat belt usage. In accordance with the sensed seating condition, a control unit determines the timing of the inflation, gas pressure in the air bag, quantity of gas in the air bag, and the position of the air bag in relation to the occupant. This system has the drawbacks of being an extraordinarily heavy, complex, and costly system.
U.S. Pat. No. 5,411,289 discloses an air bag system with a multiple-level gas generation source that inflates the air bag with a selected level of gas. The gas level and inflation sequence times are controlled by an electronic control unit which is responsive to attached temperature, seat belt, and acceleration sensors.
The two patented systems cited immediately above provide varying gas generator output; however, there is no provision for varying air bag volume. Although they provide some adjustment in aggressivity, they are not designed to cover vast differences in required protection as occur, for instance, with a 12 mph crash speed with belted occupant versus a 30 mph crash speed with unbelted occupant. The above-cited patents pertain to what are hereinafter referred to as fixed-volume, variable-inflation designs.
In summary, all of the above-cited inventions attempt to address the problems associated with the large, high aggressivity air bag by varying degrees and means. However, an air bag system is needed that fully addresses those problems and provides optimum protection regardless of whether the occupant is wearing a seat belt and whether the crash speed is moderate or severe. Further, the needs should be met with an air bag system that is simple in construction, economical to install, and compatible with existing equipment.